The invention relates to new mono-, oligo- and poly-3-(1,1-difluoroalkyl)thiophenes, polymerisable liquid crystal materials and anisotropic polymer film, including their oxidatively or reductively doped forms. The invention further relates to methods of their preparation, their use as semiconductors or charge transport materials in optical, electrooptical or electronic devices including field effect transistors, electroluminescent, photovoltaic and sensor devices. The invention further relates to field effect transistors and semiconducting components comprising the new mono-, oligo- and poly-3-(1,1-difluoro-alkyl)thiophenes. Furthermore the invention relates to a security marking or device and to a charge injection layer, planarising layer, antistatic film or conducting substrate or pattern.
Organic materials have recently shown promise as the active layer in organic based thin film transistors and organic field effect transistors (OFETs) [see reference 1]. Such devices have potential applications in smart cards, security tags and the switching element in flat panel displays. Organic materials are envisaged to have substantial cost advantages over their silicon analogues if they can be deposited from solution, as this enables a fast, large-area fabrication route.
The performance of the device is principally based upon the charge carrier mobility of the semiconducting material and the current on/off ratio, so the ideal semiconductor should have a low conductivity in the off state, combined with a high charge carrier mobility ( greater than 1xc3x9710xe2x88x923 cm2 Vxe2x88x921 sxe2x88x921). In addition, it is important that the semiconducting material is relatively stable to oxidation i.e. it has a high ionisation potential, as oxidation leads to reduced device performance.
A known compound which has been shown to be an effective p-type semiconductor for OFETs is pentacene [see reference 2]. When deposited as a thin film by vacuum deposition, it was shown to have carrier mobilities in excess of 1 cm2 Vxe2x88x921 sxe2x88x921 with very high current on/off ratios greater than 106. However, vacuum deposition is an expensive processing technique that is unsuitable for the fabrication of large-area films.
Regioregular poly(3-hexylthiophene) has been reported with charge carrier mobility between 1xc3x9710xe2x88x925 and 4.5xc3x9710xe2x88x922 cm2 Vxe2x88x921 sxe2x88x921, but with a rather low current on/off ratio (10-103) [see reference 3]. In general, poly(3-alkylthiophenes) show good solubility and are able to be solution processed to fabricate large area films. However, poly(3-alkylthiophenes) have relatively low ionisation potentials and are susceptible to doping in air [see reference 4].
Fluorinated poly(alkylthiophenes) were studied by L. Robitaille and M. Leclerc [see reference 5]. However, poly(3xe2x80x2-perfluorohexylterthiophene was found to be insoluble and poly[3-(tridecafluorononyl)thiophene] to be soluble in octafluorotoluene, a solvent unsuitable for large scale solution processing. Compared to its alkyl analogues, however, it exhibits inferior electronic properties, which was attributed to lower regioregularity. In addition, the bulky fluoroalkyl group dilutes the macroscopic charge transport mobility arising from the conjugated pi-electron component of the molecule. This large group also potentially disrupts the closely packed lammelar morphology, again lowering mobility.
Perfluoro-xcex1-sexithiophene and xcex1,xcfx89-diperfluorohexylsexithiophene are described as potential n-type semiconductors [see references 6, 7]. In fact, the xcex1,xcfx89-substituted sexithiophene exhibits carrier mobilities of up to 2xc3x9710xe2x88x922 cm2 Vxe2x88x921 sxe2x88x921 for electron transport (n-type semi-conduction). However, both fluorinated sexithiophenes have low solubilities in common solvents, and therefore may not be solution processed.
A perfluoralkylated heteroaromatic polymer represented by the general formula 
wherein R is H or alkyl, X is S, NH or O and n is 1 to 9, having a polymerization degree of 5 to 5000 is proposed in the EP 0 414 906 A1 [reference 8]. The polymer may be used as water- and oil-repellent and as an electrically conductive material. But again, the perfluoralkylated thiophenes show in general a low to very low solubility, especially in those organic solvents, which are commonly used in large scale production techniques.
It is the aim of the present invention to provide new materials for use as semiconductors or charge transport materials, which are easy to synthesize, have high charge mobility, good processibility especially a good solubility, and a good oxidative stability.
Further aims of the present inventions relate to advantageous uses of the mono-, oligo- and polymers, including their oxidatively or reductively doped forms, according to the invention.
Other aims of the invention are immediately evident to those skilled in the art from the following description.
The inventors have found that these aims can be achieved by providing new oligomers and polymers based on regioregular 3-(1,1-difluoro-alkyl)thiophenes, especially with a head-to-tail orientation. These oligo- and polymers exhibit a high degree of planarity in the backbone and strong interchain xcfx80xe2x80x94xcfx80 stacking interactions making them effective charge transport materials with high charge carrier mobilities. The electron withdrawing 1,1-difluoro group adjacent to the thiophene ring lowers the HOMO (highest occupied molecular orbit) relative to the unfluorinated poly(3-alkyl)thiophenes. The oligo- and polymers according to the invention possess a sufficient high ionization potential and are sufficiently stable to oxidation. On the other side, these oligo- and polymers possess a good to very good solubility, especially in common organic solvents. Therefore the oligo- and polymers according to the invention are amenable to fast and economically favorable solution processing.
A further aspect of the invention relates to reactive mesogens consisting of a central core comprising one or more 3-(1,1-difluoro-alkyl)thiophene units, and optionally comprising further conjugated moieties that form an extended conjugated system together with the 3-(1,1-difluoro-alkyl)thiophene units, said core being linked, optionally via a spacer group, to one or two polymerisable groups. The reactive mesogens can induce or enhance liquid crystal phases or are liquid crystalline themselves. They can be ordered and aligned in their mesophase and the polymerisable group can be polymerised or crosslinked in situ to form coherent polymer films with a high degree of long range order, or monodomain, thus yielding improved semiconductor materials with high stability and high charge carrier mobility.
A further aspect of the invention relates to liquid crystal polymers, in particular liquid crystal side chain polymers obtained from the reactive mesogens according to the present invention, which are then further processed e.g. from solution as thin layers for use in semiconductor devices.
A further aspect of the invention relates to the mono-, oligo- and polymers, a material or polymer film according to the invention, which are oxidatively or reductively doped to form conducting ionic species. Another aspect of the invention is a charge injection layer, planarising layer, antistatic film or conducting substrate or pattern for electronic applications or flat panel displays, comprising mono-, oligo- or polymers, a material or polymer film according to this invention.
Definition of Terms
The terms xe2x80x98liquid crystalline or mesogenic materialxe2x80x99 or xe2x80x98liquid crystalline or mesogenic compoundxe2x80x99 means materials or compounds comprising one or more rod-shaped, lath-shaped or disk-shaped mesogenic groups, i.e. groups with the ability to induce liquid crystal phase behaviour. The compounds or materials comprising mesogenic groups do not necessarily have to exhibit a liquid crystal phase themselves. It is also possible that they show liquid crystal phase behaviour only in mixtures with other compounds, or when the mesogenic compounds or materials, or the mixtures thereof, are polymerised.
The term xe2x80x98polymerisablexe2x80x99 includes compounds or groups that are capable of participating in a polymerisation reaction, like radicalic or ionic chain polymerisation, polyaddition or polycondensation, and reactive compounds or reactive groups that are capable of being grafted for example by condensation or addition to a polymer backbone in a polymeranaloguous reaction.
The term xe2x80x98filmxe2x80x99 includes self-supporting, i.e. free-standing, films that show more or less pronounced mechanical stability and flexibility, as well as coatings or layers on a supporting substrate or between two substrates.
The invention relates to mono-, oligo- and polymers comprising at least one 3-(1,1-difluoro-alkyl)thiophene group.
The invention further relates to the use of mono-, oligo- and polymers according to the invention as semiconductors or charge transport materials, in particular in optical, electrooptical or electronic devices, like for example in field effect transistors (FET) as components of integrated circuitry, as thin film transistors in flat panel display applications or for Radio Frequency Identification (RFID) tags, or in semiconducting components for organic light emitting diode (OLED) applications such as electroluminescent displays or backlights of e.g. liquid crystal displays, for photovoltaic or sensor devices, as electrode materials in batteries, as photoconductors and for electrophotographic applications like electrophotographic recording.
The invention further relates to a field effect transistor, for example as a component of integrated circuitry, as a thin film transistor in flat panel display applications, or in a Radio Frequency Identification (RFID) tag, comprising one or more mono-, oligo- or polymers according to the invention.
The invention further relates to a semiconducting component, for example in OLED applications like electroluminescent displays or backlights of e.g. liquid crystal displays, in photovoltaic or sensor devices, as electrode materials in batteries, as photoconductors and for electrophotographic applications, comprising one or more mono-, oligo- or polymers according to the invention.
The invention further relates to a security marking or device comprising an RFID or ID tag or a FET according to the invention.